The speeds advertised by internet providers are notoriously optimistic. They assume an optimum connection to sites capable of providing the highest speed downloads. So while 35Mb may be the advertised speed, around half that speed will be typical, particularly when accessing popular sites or at busy times of the day such as mornings and between 7pm and 11pm in the evening when loads are highest. It may not be your end of the connection that is slow, just the system at the other end of the line struggling to deal with all the requests for data.
Don't forget that when speeds are written as 35Mb per second, the internet provider actually means 35 mega bits per second, not bytes; so eight times slower than you might be expecting.
The latest generation of modems usually take a couple of days or so to tune themselves to your usage patterns and the line characteristics to the exchange. Even optical fibre signals suffer errors and interference that needs correcting.
Then of course it takes time for your computer to actually react to the influx of information. If you can sustain a couple of HD streams on two different computers in the home without stuttering, that is probably as good as you can expect from consumer grade kit. Anything better, you need permanent leased lines and a very fat wallet.